Apex domains cannot have CNAME records.
Question and response
Question
dig spamtitan.com. NS
Answer
spamtitan.com. 5 NS ns-1897.awsdns-45.co.uk.
spamtitan.com. 5 NS ns-515.awsdns-00.net.
spamtitan.com. 5 NS ns-94.awsdns-11.com.
spamtitan.com. 5 NS ns-1365.awsdns-42.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0